def _serialize(self, value, attr, obj):
        general_names = []
        name_type = None

        if value:
            for name in value._general_names:
                value = name.value

                if isinstance(name, x509.DNSName):
                    name_type = "DNSName"

                elif isinstance(name, x509.IPAddress):
                    if isinstance(value, ipaddress.IPv4Network):
                        name_type = "IPNetwork"
                    else:
                        name_type = "IPAddress"

                    value = str(value)

                elif isinstance(name, x509.UniformResourceIdentifier):
                    name_type = "uniformResourceIdentifier"

                elif isinstance(name, x509.DirectoryName):
                    name_type = "directoryName"

                elif isinstance(name, x509.RFC822Name):
                    name_type = "rfc822Name"

                elif isinstance(name, x509.RegisteredID):
                    name_type = "registeredID"
                    value = value.dotted_string
                else:
                    current_app.logger.warning(
                        "Unknown SubAltName type: {name}".format(name=name)
                    )
                    continue

                general_names.append({"nameType": name_type, "value": value})

        return general_names